1. Field of the Invention
The present invention relates to a field of the chaotic signal-aided spread-spectrum communications.
The present invention relates to the field of the spread spectrum transmission of information, which is performed by chaotic signals. In particular, the present invention relates to the method for direct chaotic communications with pre-determined spectral mask.
2. Description of the Related Art
At present, it is known that chaotic signals generated by non-linear deterministic dynamic systems, the so-called dynamic chaos, possess a number of properties that make such signals suitable for transmission of information. In particular, the promising nature of chaotic signals as carrier or modulating oscillations is shown (A. S. DMITRIEV, A. I. PANAS, S. O. STARKOV. Dynamic chaos as a paradigm for modern telecommunication systems//Uspekhi Sovremennoy Radielektroniki, 1997, #10, p. 4; M. HASLER. Achievements in the field of information transmission with the use of chaos//Uspekhi Sovremennoy Radielektroniki, 1998, #11, p. 33). Certain information transmission circuits using the dynamic chaos are proposed, in particular, a circuit of information signal chaotic masking (L. KOCAREV, K. S. HALLE, K. ECKERT, L. CHUA, U. PARLITZ. Experimental demonstration of secure communications via chaotic synchronization//Int. J. Bifurcation and Chaos, 1992, v. 2, #3, p. 709), a circuit with chaotic modes switching [H. DEDIEU, M. KENNEDY, M. HASLER. Chaos shift keying: Modulation and demodulation of a chaotic carrier using self-synchronizing Chua's circuits//IEEE Trans. Circuits and Systems, October 1993, v. CAS-40, #10, p. 634], circuits with non-linear mixture of information signal to chaotic signal (A. R. VOLKOVSKI, N. V. RULKOV. Synchronous chaotic response of non-linear system used to transmit information with a chaotic carrier//Letters to Zhurn. Techn. Fiz., 1993, v. 19, #3, p. 71; A. DMITRIEV, A. PANAS, S. STARKOV. Experiments on speech and music signals transmission using chaos//Int. Journal of Bifurcation and Chaos, 1995, v. 5, p. 371) etc. Under consideration are possibilities of generating direct chaotic communication systems with chaotic oscillations serving as an information carrier generated within the frequency band where transmission of information takes place, for example, in microwaves (A. S. DMITRIEV, B. E. KYARGINSKI, N. A. MAKSIMOV, A. I. PANAS, S. O. STARKOV. Prospects of creating direct chaotic communication systems in RF and microwave bands//Radiotekhnika, 2000, #3, p. 9).
There are two varieties of methods for spread-spectrum communications. The first uses a narrow-band periodic carrier of information, e.g., code-division multiple-access system (CDMA), as well as the systems with frequency modulation, where the frequency band of the transmitted information is essentially narrower than the frequency band of the carrier signal. The other variety of the methods for spread-spectrum communications uses a principally wide-band carrier, whose frequency band is wider than the frequency band of the transmitted information (U.S. Pat. No. 16,097, H04K1/00, Mar. 18, 1960). Frequency-hopping spread-spectrum systems should also be referred to this variety (J. PROAKIS. Digital Communication, McGraw-Hill, Inc., New-York, 1995, p. 741).
The closest to the method described in the present invention is the frequency-hopping spread-spectrum communication method. Under this method, the transmitting side generates a wide-band information carrier within a preset information transmission frequency band; the carrier is modulated by means of information signal; the modulated signal is transmitted via a communication channel from the transmitting side to the receiving side that demodulates the received information carrier to retrieve the information signal (see the above mentioned monograph of J. PROAKIS).
As distinct from this, in the present invention a wide-band information carrier is generated with the help of a chaotic dynamic system that generates chaotic signals directly within the entire frequency band of information transmission (e.g., within a microwave band). In order to use the above signals as a wide-band carrier, it is necessary to solve the problem of generating chaotic oscillations within the required frequency band of electromagnetic spectrum, as well as to elaborate effective methods for information input into the chaotic signal on the transmitting side and for extracting it out of the said signal on the receiving side. By present, only directions of developing the systems based on such a principle have been outlined, yet not their particular microwave implementations (see the above mentioned article by A. S. DMITRIEV in Radiotekhnika Magazine).
At present it is known that chaotic signals generated by nonlinear deterministic dynamic systems (the so-called dynamic chaos) possess a number of features that stimulate application of such signals in communications:
possibility of obtaining complex oscillations in simple-structure devices;
possibility of obtaining many different chaotic modes in a single device;
possibility of effective control of chaotic modes by means of small variation of system parameters;
large information capacity;
capability of self-synchronization of transmitter and receiver;
alternative methods of multiplexing; and
confidentiality of information transmission.
In particular, promising is shown the use of chaotic signals generated by the so-called chaotic dynamic systems as carrier or modulated oscillations (Dmitriev, A. S. et al., “Dynamic chaos as paradigm for contemporary communication systems,” Uspekhi sovremennoi radioelektroniki, 1997, No. 10, p. 4; Hasler, M., “Advances of communications using chaos”, Uspekhi sovremennoi radioelektroniki, 1998, No. 11, p. 33; A. S. Dmitriev, A. I. Panas, Dynamic Chaos. Novel Information Carriers for Communications.—Fizmatlit, Moscow, 2002). A number of concrete schemes for transmission of information using dynamic chaos are proposed, in particular, a scheme with chaotic masking of information signal (L. Kosarev, K. S. Halle, K. Eckert, L. Chua, U. Parlitz, Experimental demonstration of secure communications via chaotic synchronization, Int. J. Bifurcation and Chaos, 1992, v. 2, No 3, pp. 709-713), a scheme with chaos shift keying (H. Dedieu, M. Kennedy, M. Hasler, Chaos shift keying: Modulation and demodulation of a chaotic carrier using self-synchronizing Chua's circuits, IEEE Trans. Circuits and Systems, October 1993, v. CAS-40, No 10, pp. 634-642), a scheme with nonlinear mixing of information signal to chaotic one (Volkovsky, A. R., Rulkov, N. V., “Synchronous chaotic response of nonlinear information transmission system using chaotic carrier,” Pis'ma v Zhurn. Tekhn. Fiz., 1993, vol. 3, no. 3, pp. 71-75; A. Dmitriev, A. Panas, S. Starkov, Experiments on speech and music signals transmission using chaos, Int. Journal of Bifurcation and Chaos, 1995, v. 5, No 3, pp. 317-376), etc. Direct chaotic communications scheme is proposed, in which chaotic oscillations play the role of information carrier, said carrier being generated directly in the frequency range used for the transmission of information, e.g., in microwave band (Dmitriev A. S., Kyarginsky B. E., Maksimov N. A., Panas A. I., Starkov S. O., “Prospects of constructing direct chaotic communication systems for RF and microwave bands,” Radiotekhnika, 2000, No. 3, pp. 9-19).
There are two varieties of methods for spread spectrum transmission of information. The first uses narrowband information carrier. Examples are code-division multiple-access systems, CDMA, that use Direct Sequence Spread Signals; and systems with frequency modulation in which the frequency bandwidth of the transmitted information is essentially less than the bandwidth of the transmitted signal. In the other variety of methods for spread spectrum transmission of information a novel wideband carrier is used, whose frequency bandwidth is greater than the transmitted information bandwidth (U.S. Pat. No. 4,363,130, issued Dec. 7, 1982). Frequency-Hopping Spread Spectrum systems also refer to this variety (J. Proakis, Digital Communication, McGraw Hill, Inc., New York, 1995).
The related art that is most close to the method of this invention is the method for transmission of information using chaotic signals, in which: at the transmitting side of each user an information carrier is formed in at least a part of the predetermined frequency range, wherein said information carrier is formed with a chaotic dynamic system, which structure is synthesized in advance according to predetermined characteristics of said information carrier; in synthesizing said chaotic dynamic system, regions of its parameters are revealed that provide the same type behavior of said chaotic dynamic system; from said revealed parameter regions, values of parameters of said chaotic dynamic system are chosen so as to provide forming of said information carrier in the form of chaotic information carrier with at least predetermined spectral characteristics; said formed information carrier is modulated by corresponding information signal; the modulated chaotic information carrier is transmitted through communication channel to the receiving side; at the receiving side of each user the step of reception and demodulation of received chaotic information carrier is performed using a dynamic system matched in its behavior with said chaotic dynamic system of the transmitting side (Patent of Russian Federation No. 2185032, N 04 K 1/10, Oct. 7, 2002). This method allows effective use of ultrawide band of carrying chaotic signal for organization of high-rate communications channels.
However, this method does not imply any other restrictions on the power spectrum of the signal formed and transmitted through the channel, except its bandwidth. In particular, it doesn't impose restrictions on the spectral density. At the same time, there is a need in methods for communications with restricted power spectral density, e.g., by development of new communications standards.